1. Field of the Invention
The invention relates to a device for gripping containers from above.
2. Description of the Related Art
Container gripping devices are generally known and, because the frame is generally adjustable, are usually referred to as spreaders.
Spreaders are applied for gripping containers during hoisting thereof, for instance during loading or unloading of container ships. Standard containers are provided for handling and anchoring thereof with gripping points on the corners, so-called corner castings. These corner castings form reinforced corner points in which an elongate opening is formed. The gripping means of the frame, usually in the form of a so-called twist-lock, can grip in these openings.
A twist-lock consists here of a pin or shank with a hammer head on an outer end, which pin is received at its other outer end in a bush or sleeve, which is connected in turn to a rotating operating mechanism. The twist-lock can be rotated through 90 degrees by the operating mechanism between a position in which the hammer head can be placed in the elongate opening and a position in which the hammer head is fixed in this opening.
Since during loading and unloading of containers the transport means on which or in which the containers are supplied and/or removed necessarily stands or lies still, the time involved herein is in principle costly for the transporter. It is therefore of great importance that this time is minimized by processing the containers as quickly as possible. This entails gripping devices being carried to the containers at increasingly higher speed and hoisting speeds increasing more and more.
Owing to these higher speeds the loads which occur when the frame of the gripping device lands on the container are also becoming increasingly larger. These greater loads result in increased wear and thus a reduction in the life span of the different components of the device, while in addition the high loads result in considerable noise production, both during landing of the frame on the container and at the beginning of the hoisting movement, when the device is not yet fully loaded. This noise results in nuisance, particularly in built-up areas.
It has already been proposed to reduce the loads on the gripping device, and thereby the noise nuisance, by applying spring-mounting and/or damping. There are therefore spreaders on the market wherein each twist-lock with its operating mechanism is accommodated in a housing, which is movable in resilient and/or damped manner in the direction of load relative to the frame, thus parallel to the shank of the twist-lock. In one of the known spreaders rubber blocks arranged between the housing and the frame are used as spring and/or damping elements, while in another known design use is made of hydraulic cylinders.
These known spreaders have the drawback that space is required for guiding of the housing in the frame, whereby the outer dimensions of the frame become larger at the position of the corners, and the frame will therefore protrude outside the container(s). All lateral loads will hereby be absorbed by the frame, so that the chance of damage to the gripping device increases.
The spring and/or damping elements also take up space above the twist-locks, whereby the construction height of the frame increases. This has consequences for the driving of the pivotable centring members or “flippers” usually arranged on the corners of the frame. Because this drive is usually arranged on top of the frame, an increase in the frame height results in a greater distance of the flippers from the drive, and therefore a greater moment arm, so that the drive has to take a heavier form.
The stability of the construction is furthermore reduced by the floating suspension of the twist-locks, while the precision with which the spreader can be placed on a container likewise decreases.
Finally, owing to the increase in the dimensions of the frame in all directions, the chance of damage thereto is increased disproportionately, since a spreader in loaded state, particularly when it is hoisting a plurality of containers simultaneously, will never hang perfectly horizontally. A slightly inclining position, particularly at the start of a hoisting movement, can result in the spreader becoming jammed, for instance in a cell of a container ship, whereby very high loads will occur which will soon result in damage.